i would start with measuring the acoustics in your room, and get that right first. Then I don’t think you can use cash as a yardstick for improvement, it is subjective. Start with speakers and amp that match, a good pre or integrated, and then your sources. As for cables power first, interconnects second, speaker wire third. I would allocate more budget to the top of that list and then work your way to the end as time and budget allow. These days expensive is not always good and good is not always expensive,